1. Field of the Invention
This invention relates to new isocyanate derivatives containing carbodiimide and sulfonate groups, to a process for their production by the at least partial carbodiimidization of organic polyisocyanates followed by reaction of any free isocyanate groups still present with compounds containing isocyanate-reactive groups (the starting materials and/or reactants used being inter alia compounds containing sulfonate groups) and to the use of the isocyanate derivatives containing sulfonate groups as additives for aqueous dispersions or solutions of plastics containing incorporated carboxyl groups and/or incorporated groups convertible to carboxyl groups.
Description of the Prior Art
Aqueous solutions or dispersions of ionically modified plastics are known in large numbers. Thus, the production of polyurethane dispersions or solutions optionally containing urea groups is described, for example, in DE-PS Nos. 1,178,586, 1,184,946, DE-OS Nos. 1,495,745, 1,770,068, 2,314,512, 2,446,440, 2,543,091, 2,642,073, U.S. Pat. Nos. 3,480,592, 3,388,087, 3,479,310, 3,756,992, 3,905,929 and in "Angewandte Chemie" 82, 53 et seq (1970).
The production of aqueous or water-dilutable polycondensates, more especially polyester resins, optionally containing organic solvents and/or urethane groups, is also known (cf. DE-OS No. 2,225,646, DE-AS No. 2,239,094, DE-OS No. 2,446,439, U.S. Pat. Nos. 3,876,582, 4,029,617, cf. also Houben-Weyl "Methoden der Organishen Chemie" XIV/2 (1963), pages 30 et seq).
The production of polymers, more especially polyacrylates, containing incorporated ionic groups is also known (cf. for example Houben-Weyl "Methoden der Organischen Chemie" XIV/1 (1961), pages 103 et seq or XIV/2 (1963), page 754).
The solubility or dispersibility of these plastics in water is often ensured by carboxylate groups chemically incorporated in the plastics which contain as counterions ammonium cations based on ammonia or thermally volatile organic amines. When drying the sheet-form materials (coatings) produced from solutions and, more especially, dispersions of the type in question (which is generally carried out by heating), many of the carboxylate groups originally present are converted into carboxyl groups through elimination of the ammonia or amine counterion, the carboxyl-containing plastics then present often show unsatisfactory resistance to water. In addition, these carboxyl groups catalytically accelerate the obviously undesirable hydrolytic degradation of plastics containing ester groups which can result in rapid deterioration of the mechanical properties of the above-mentioned sheet-form materials, especially in a damp atmosphere.
Accordingly, the object of the present invention is to provide an additive for aqueous solutions and, more especially, dispersions of plastics containing carboxyl groups and/or carboxylate groups convertible into carboxyl groups which ensures that, before or during drying of the sheet-form materials produced from the solutions or dispersions, the carboxyl groups are converted into largely non-hydrophilic groups which have no catalytic effect on the hydrolytic degradation of any ester groups present in the plastics. At the same time, the conversion of the carboxyl groups into the non-hydrophilic groups mentioned is to be accompanied by crosslinking of the sheet-form material in order thus to improve its mechanical properties and, in particular, its wet strength.
This object is achieved by providing isocyanate derivatives containing carbodiimide groups according to the invention which are described in more detail hereinafter. Although hydrophilic groups are also present in the isocyanate derivatives according to the invention, the concentration in which they are present is generally considerably lower so that, through the use of the additives according to the invention, the hydrophilicity of the plastics can be very considerably reduced (i) by reducing the total concentration of hydrophilic groups and (ii) through the crosslinking effect mentioned above.